In his remarks, Romney is expected to brand the billionaire businessman as "a phony, a fraud" whose "promises are as worthless as a degree from Trump University."

The cable news networks on Thursday are expected to air live coverage of Mitt Romney's speech, in which the former Republican presidential nominee is expected to give GOP candidate Donald Trump a verbal lashing.

Among the cable news networks expected to cover Romney's remarks, CNN has been teasing the speech with a graphics like the one reading "Next Hour: Romney Speaks on 2016 Race." MSNBC is promoting "Romney Speaks Out Against Trump" in an onscreen graphic, and Fox News Channel's anchor also is teasing live coverage of the speech, which is planned to begin at 8:30 a.m. PT at the University of Utah.

In his remarks, Romney will brand the billionaire businessman as "a phony, a fraud" whose "promises are as worthless as a degree from Trump University," according to The Associated Press, which obtained excerpts of his remarks in advance.

Trump, in turn, has dismissed Romney as "a stiff" who "didn't know what he was doing" as the party's candidate in 2012 and blew a chance to beat President Barack Obama. "People are energized by what I'm saying" in the campaign and turning out in remarkable numbers to vote, Trump told NBC's Today.

In ratcheting up the rhetoric, Romney cast his lot with a growing chorus of anxious Republican leaders — people many Trump supporters view as establishment figures — in trying to slow the New York real estate mogul's momentum.

"Here's what I know: Donald Trump is a phony, a fraud," the former Massachusetts governor said, according to the early excerpts.

But it was unclear what impact his words would have with voters deeply frustrated by their party's leaders, and Romney is not using the speech to endorse a Trump rival. Trump questioned whether the party rank and file would listen to "a failed candidate" for whom "nobody came out to vote."

Thursday's condemnation and counter comes four years after the two men stood side by side in Las Vegas, with Trump saying it was a "real honor and privilege" to endorse Romney's White House bid. Accepting, Romney said it was a "delight" to have Trump on his side and praised him for ability to "understand how our economy works and to create jobs for the American people."

Panicked GOP leaders say they still have options for preventing Trump from winning the GOP nomination — just not many good ones.

Romney also said that a Trump nomination at the party's convention in Cleveland in July would enable Democrat Hillary Clinton to win the presidency. He contended that Trump "has neither the temperament nor the judgment to be president."

Romney's involvement comes as party elites pore over complicated delegate math, outlining hazy scenarios for a contested convention and even flirting with the long-shot prospect of a third-party option.

Giving Romney the back of his hand, Trump turned his sights on the general election. His campaign reached out to House Speaker Paul Ryan's office to arrange a conversation between the two men, and urged Republican leaders to view his candidacy as a chance to expand the party.

Trump padded his lead with victories in seven Super Tuesday contests, with Texas Sen. Ted Cruz claiming three states and Florida Sen. Marco Rubio picking up his first victory of the 2016 race.

Despite Trump's strong night, he was not yet on track to claim the nomination before the party's national gathering in July, according to an Associated Press delegate count. He has won 46 percent of the delegates awarded so far, and he would have to increase that to 51 percent in the remaining primaries.

GOP strategists cast March 15 as the last opportunity to stop Trump through the normal path of winning states and collecting delegates. A win for Rubio in his home state of Florida would raise questions about Trump's strength, as could a win for Kasich, Ohio's governor, on his home turf.

The candidates have a high-profile opportunity to make their case to voters in Thursday night's primetime debate. Retired neurosurgeon Ben Carson all but ended his bid Wednesday, saying he would skip the debate and declaring he did "not see a political path forward."

The GOP mayhem contrasted sharply with a clearer picture on the Democratic side, where Hillary Clinton was drawing broad support from voters and her party's leaders. Rival Sen. Bernie Sanders vowed to keep up the fight, though his path to the nomination has become exceedingly narrow.

Romney argues that Trump's "domestic policies would lead to recession. His foreign policies would make America and the world less safe," Romney says. "And his personal qualities would mean that America would cease to be a shining city on a hill."

The Associated Press has asked Republican governors and senators if they would support Trump if he becomes the party's nominee. Of the 59 respondents, slightly fewer than half could not commit to backing him in November.

One long-shot idea rumbling through power corridors in Washington was the prospect of a late third-party candidate to represent more mainstream conservatives. Former Texas Gov. Rick Perry has been approached by "a mixture of people" about being part of a third-party bid, according to Jeff Miller, who managed Perry's failed GOP presidential campaign. But Miller said Perry found the idea "ludicrous."